The present invention relates to a process and an apparatus for producing a hollow molded article by a blow molding process. More specifically, the present invention directs to a process and an apparatus for production of hollow molded articles such as resin ducts and hoses as a final product by cutting unnecessary portions of an intermediate molded article, particularly, by cutting an end of the intermediate molded article in a mold intermittently or successively in a blow-molding step.
A cylindrical hollow article such as resin tube, hose and duct is conventionally produced by blow-molding a molten resin parison in a mold. The blow-molding processes comprise a step for setting a resin parison excluded from a die in a cavity formed by a pair of metal mold-members, a step for closing molding members, and a step for blowing a pressurized air into the resin parison to expand and form a hollow product. The molding of such hollow articles produces unnecessary portions or sites at the ends of the final product. Thus, the unnecessary portion in the final product is usually formed at the closed or narrow end of the final product.
Therefore, after taking out the intermediate hollow product from the metal mold, the unnecessary portion of the intermediate hollow product is cut manually by using a cutting means such as knife to produce a cylindrical hollow product. However, this cutting operation increases a production cost, and forms an irregular end surface on the cutting face, since the manual cutting operation is conducted individually outside the metal mold of the blow-molding apparatus. Thus, the finishing process for the cut irregular face is required, and the productivity of the hollow articles would be reduced.
It is, therefore, an object of the present invention to provide a process and an apparatus for producing a hollow product or article by cutting efficiently an unnecessary portion(s) of an intermediate hollow product in a molding process without cutting operations after blow-molding.
It is another object of the present invention to provide a process and an apparatus for producing a hollow product or article with improving productivity and reducing production cost.
The inventor of the present invention did intensive investigation to achieve the above objects, and found that use of a cutting means movable forwardly and backwardly in a metal mold relative to an intermediate product improves the cutting efficiency of unnecessary portions of the intermediate product to produce high quality hollow products stably. The present invention is based on the above finding.
Thus, a process for producing a hollow molded article having an open end by blow-molding method, which comprises a setting step for setting or putting a resin parison in cavity formed by a pair of metal mold members, a blowing step for blowing a pressurized gas (a compressed gas) into the resin parison to form an intermediate molded article, and a cutting step for cutting a predetermined part or section (i.e. cutting site) from the intermediate molded article with forward or backward movement of a cutting means which is movable crossly the cavity. In the process, the predetermined part or portion of the intermediate molded article is cut with a cutting means which is attached movably to the one member of the metal mold members. The cutting means may be movable reciprocally in a cross direction relative to the longitudinal or axial direction of the cavity or the metal mold members. The cutting means may be guided movably along a groove or slit formed in the metal mold members, and the predetermined part (or cutting site) of the intermediate molded article is cut with the cutting means The cutting means may comprise a blade being crossable (traversable) in an across direction relative to the longitudinal or axial direction of the intermediate molded article to be cut, and at least one end of the intermediate molded article is cut by the blade of the cutting means. The invention further discloses a process for cutting an unnecessary portion(s) of a hollow molded article in a metal mold. This process may comprise setting a resin parison in cavity formed by a pair of metal mold members, blowing a pressurized gas into the resin parison for expansion or inflation to form an intermediate molded article, and cutting a predetermined part or portion of the intermediate molded article with forward movement of a blade of a cutting means which is movable crossly the cavity.
A blow-molding apparatus of the invention is used for producing a hollow molded article. The apparatus may comprise a pair of metal mold members which are openable or closable each other and are formable a cavity for accommodating a resin parison, a blowing means for blowing a pressurized gas into the resin parison to form an intermediate molded article, a cutting means, which is movable crossly the cavity, for cutting a predetermined part (i.e. cutting site) of the intermediate molded article, and a reciprocating means for reciprocating the cutting means.
The inner wall of the metal mold members may have a groove or slit extending to a cross direction relative to the axial direction of the intermediate molded article, and the cutting means may comprise a cutter unit for cutting the intermediate molded article and an actuating means (e.g. cylindrical actuating means) for actuating the cutter unit forward or backward direction along the groove or slit. The groove or slit may be formed at a position of the inner wall corresponding to an end or edge of a final molded article. Further, the cutter unit has a various blade such as a circular hollow blade being acceptable the setting or accommodation of the resin parison, at least an inclined or curved blade which contacts pointedly or linearly substantially with the surface of the intermediate molded article, and so on. The blow-molding apparatus may further comprise a stopper being displaceable forward or backward against (or along axial direction of) an end of the resin parison and closable tightly the end of the resin parison in association with the mold members, and a control unit for controlling the forward or backward movement of the cutting means in response to the backward or forward movement of the stopper relative to the intermediate molded article. In the operations by the control unit, the forward displacement of the stopper regulates the advancement of the cutting means and the backward displacement of the stopper allows to move the cutting means forward.